Shane doesn't go sober because not everyone needs to.

Shane fell into the beginnings of a dangerous pattern of binge drinking because of his untreated depression.

When he sought treatment in the city, he set healthy boundaries about drinking only in the evenings and not to excess.

This is not the same problem Pam has. Pam is not able to set those healthy boundaries even when she tries.

If everyone who drank too much as a depressed young adult had to be branded an alcoholic for life, that would be most of the people you know.